Electrical telegraph

An electrical telegraph is a telegraph that uses electrical signals, usually conveyed viatelecommunication lines or radio. The electromagnetic telegraph is a device for human-to-human transmission of coded text messages.

The electrical telegraph, or more commonly just 'telegraph', superseded optical semaphore telegraph systems, such as those designed by Claude Chappe for the French military, and Friedrich Clemens Gerke for the Prussian military, thus becoming the first form of electrical telecommunications. In a matter of decades after their creation, electrical telegraph networks permitted people and commerce to almost instantly transmit messages across both continents and oceans, with widespread social and economic impacts.

History

Early works and messages

From early studies of electricity, electrical phenomena were known to travel with great speed, and many experimenters worked on the application of electricity to communications at a distance.

All the known effects of electricity - such as sparks, electrostatic attraction, chemical changes,electric shocks, and in later, more advanced studies, electromagnetism - were applied by various people to the problems of detecting controlled transmissions of electricity at various distances.

In 1746 the French scientist and abbé Jean-Antoine Nollet, gathered about two hundred monksinto (Don't knows what it means teacher) a circle about a mile (1.6 km) in circumference, with pieces of iron wire connecting them. He then discharged a battery of Leyden jars (device that "stores" static electricity between two electrodes on the inside and outside of a jar) through the human chain and observed that each man reacted at substantially the same time to the electric shock, showing that the speed of electricity's propagation was very high.

 Telegraphs employing electrostatic attraction were the basis of early experiments in electrical telegraphy in Europe, but were abandoned as being impractical and were never developed into a useful communication system.

In 1800 Alessandro Volta invented the Voltaic Pile, allowing for a continuous current of electricity for experimentation. 

Another very early experiment in electrical telegraphy was an electrochemical telegraph created by the German physician, anatomist and inventor Samuel Thomas von Sömmering in 1809, based on an earlier, less robust design of 1804 by Catalan polymath (is a person whose expertise spans a significant number of different subject areas) and scientist Francisco Salvá i Campillo. Both their designs employed multiple wires (up to 35) in order to visually represent almost all Latin letters and numerals. The principal disadvantage to the system was its prohibitive cost, due to having to manufacture and string-up the multiple wire circuits it employed, as opposed to the single wire (with ground return) used by later telegraphs.

In 1816, Francis Ronalds set up a primitive telegraph. He ran eight miles (13 km) of cable (encased in glass tubing) through his back garden suspending it from two wooden lattices. and succeeded in getting an electrical signal along the full length using static high voltage electricity. At both ends there were clockwork operated dials with numbers and letters of the alphabet.

Hans Christian Ørsted discovered in 1820 that an electric current produces a magnetic field which will deflect a compass needle. In the same year Johann Schweigger invented the galvanometer, with a coil of wire around a compass, which could be used as a sensitive indicator for an electric current.

In 1825 William Sturgeon invented the electromagnet, with a single winding of uninsulated wire on a piece of varnished iron, which increased the magnetic force produced by electric current. Joseph Henry improved it in 1828 by placing several windings of insulated wire around the bar, creating a much more powerful electromagnet which could operate a telegraph through the high resistance of long telegraph wires.